A light control glass containing a light control suspension was first invented by Edwin Land. The form thereof has a structure wherein a light control suspension in a liquid state is injected between two transparent electroconductive substrates having a narrow gap (see, for example, Patent Documents 1 and 2). According to Edwin Land's invention, in the state that no electric field is applied to the liquid light control suspension, which is injected between the two transparent electroconductive substrates, the great majority of incident light is reflected, scattered or absorbed on/in the light control particles dispersed in the suspension by Brownian movement of the light control particles. Only a very small portion of the light is transmitted therethrough.
In other words, the degree of the transmission, reflection, scattering or absorption is decided in accordance with the shape, nature and concentration of the light control particles dispersed in the light control suspension, and the energy quantity of the radiated light. When an electric field is applied to a light control window wherein light control glass having the above-mentioned structure is used, an electric field is formed in the light control suspension via the transparent electroconductive substrates. The light control particles, which show a light control function, are polarized so that the particles are arranged in parallel to the electric field. As a result, light is transmitted between the light control particles. Finally, the light control glass turns transparent. However, such an initial light control device has not easily been put into practice use because of the aggregation of the light control particles in the light control suspension, the sedimentation thereof based on the weight of the particles themselves, a change in the color phase on the basis of heat, a change in the optical density, a deterioration based on the radiation of ultraviolet rays, difficulties in the maintenance of the gap between the substrates and in the injection of the light control suspension into the gap, and others.
Robert L. Saxe, F. C. Lowell or R. I. Thompson discloses a light control window using a light control glass which compensates for problems of initial light control windows, that is, the aggregation and the sedimentation of light control particles, a change in the optical density, and others (see, for example, Patent Documents 3 to 9). According to these patents and others, use is made of a liquid-state light control suspension composed of light control crystal particles in a needle form, a suspending agent for dispersing the crystal particles, a dispersion adjustor, a stabilizer and others to make the density of the light control particles substantially equal to that of the suspending agent, whereby the sedimentation of the light control particles is prevented while the addition of the dispersion adjustor makes the dispersibility of the light control particles high. In this way, the aggregation of the light control particles is prevented so that the initial problems are solved.
However, the light control glass has a structure wherein a light control suspension in a liquid state is sealed into a gap between two transparent electroconductive substrates, similarly to any conventional light control glass; thus, when a large-size product is produced, it is difficult to seal the suspension evenly into the gap between the two transparent electroconductive substrates, so that there remains a problem that a difference in hydraulic pressure between the upper and lower regions of the product easily causes an expansion phenomenon of the lower region. Additionally, in accordance with the external environment, for example, the pressure of wind, the gap between the substrates is changed, so that the following problem is caused: the optical density is changed so that the color phase becomes uneven; or a sealing member, in the surroundings, for storing liquid between the transparent electroconductive substrates is broken so that the light control material leaks. Moreover, the response time becomes uneven by a deterioration based on ultraviolet rays, or a drop in the voltage between the circumferential region and the center region, of the transparent electroconductive substrates.
As a method for improving the above, suggested is a method of mixing a liquid light control suspension with a solution of a curable polymeric resin, and using a phase-separation method by polymerization, a phase-separation method by solvent-volatilization, a phase-separation method depending on temperature, or some other method to produce a film (see, for example, Patent Document 10).